A connecting piece of this kind is described in the DOS No. 25 28 757. The connecting member is inserted into the threaded member whereby an annular groove around the internal circumference of the threaded member corresponds to an annular projection on the external circumference of the connecting member. With this arrangement, the diameter of the quick-release lock is relatively small and the effective axial loading area of the connection between the two surfaces of the groove and projection, is correspondingly small. In consequence thereof are created a number of unfavourable conditions when high axial forces are present or when the media in the supply lines are streaming alternatingly in opposite directions and create pulsating loads. This is especially unfavourable when the two members of the connecting piece are made of a plastics material because the surface pressure may be so high that it resiliently expands the threaded member and elastically compresses the connecting member which is inserted into the latter, at least in the area of the annular lock. This condition may lead to the unintentional release of the lock. In addition to this there is the danger of the annular projection being torn off under shear loads resulting from an excessive surface pressure, especially with connecting pieces assembled from a threaded member made of a plastics material, and a connecting member made of metal.
Another drawback which is due to the relatively small diameter of the annular quick-release connection is explained below: The resilient expansion of the threaded member, and the elastic compression of the connecting member, aggravated by the danger of shearing the projection off, depend substantially on the choice of the materials used with the manufacture of the threaded member. It is easy to see that a threaded member consisting of metal will hardly be resiliently expanded under axial loads. However, the danger of shearing is greater, especially when the adjacent connecting member consists of a plastics material. This danger may be counteracted by a correspondingly resistant profile of the annular projection. This dependency on the structural materials makes it necessary to provide two different connecting members of different dimensions when a connecting piece is used with supply lines having different diameters, to be suitable for the threaded member which may be manufactured of metal or of a plastic material.
It is an object of the present invention to provide a connecting piece of the type referred to above which, in order to avoid the above drawbacks, is designed in such a manner that the danger of excessive axial surface pressure does not occur.
This object is solved by pushing the connecting member over the threaded member whereby the annular projection is loaded on the external circumference of the threaded member, and the annular groove extends around the internal circumference of the connecting member.
With this arrangement the location of the annular quick-release lock has been changed by moving it radially outwardly, in consequence of which the diameters of the annular groove and projection had to be increased. The axial surface pressure between the annular projection and the annular groove is therefore small even with connecting pieces subjected to high tensile loads or passing media under pulsating loads. This reduced surface pressure is too small to lead to a resilient expansion of the connecting member now located on the outside; nor does it suffice for compressing the threaded member on the inside of the assembly. Obviously the pressure is also too small to shear the annular projection off.